1. Field of Invention
The present invention generally relates to wheel-blocking devices and in particular a safety chock for large wheeled vehicles.
2. Related Art
The operators of trucks and other large wheeled vehicles are required by law or by the insurance companies to use safety devices to prevent accidents due to slipping or sliding of trucks on steep grades, slippery pavement, or when loaded by a forklift, or a crane.
It is known that for starting a large wheeled vehicle parked on a grade, the vehicle has a tendency to roll backwards before the clutch is fully disengaged. In addition, if the road is slippery, the vehicle may slide and the motor “killed” before starting the forward motion.
It is customary for truck drivers to carry blocks of wood, or metal, to be placed under the tires in the direction of the anticipated roll. This operation becomes particularly difficult for the person positioning the wheel blocks when they have to run around the truck to place the block under each wheel one at a time. This creates a potentially lethal condition for side-slipping, which may result in the truck swinging around, or in unintended movements of the vehicle that may overrun the block. In addition, there are numbers of blocks left on highways and this may lead to undesired traffic accidents. It is known that a wooden chock forgotten on the deck of a ferry was the cause of a serious accident.
Installing mechanical wheel blocks for a tractor pulling a trailer up a hill may be more demanding as the blocks have to be first applied to the more elevated wheels so as to maintain tension in the coupler and this may result in a doubling, or jack-knife action. Moreover, collecting the wheel blocks at departure time does not help the drivers' morale and includes a number of activities for loosening the blocks, as there is always a natural tendency of the vehicle to trap the blocks. The driver has to get in the cabin and start the vehicle, move the vehicle so as to loosen the wheel blocks, stop the vehicle and step out to collect the blocks, store the blocks in dedicated places, and climb back in the cabin to start the journey.
Large vehicles like trucks, tractor-trailers, and buses are provided with emergency brake systems that are actuated in the event of failure of the vehicle's normal service brake system. The emergency brake system, or the maxi-brake, may also fail due to a variety of reasons and it is considered unsafe to park a large wheeled vehicle on a grade, or slippery pavement secured with the maxi-brake only.
On some locomotives, the application of the handbrake actuates an air release valve to the brake cylinder on the side of the truck where the handbrake is operated. There have been incidents of rollaway locomotives because of the failure of this release valve. In many cases, employees have applied the handbrake and shut down the locomotives, only to discover later that the handbrake was not applied after the air leaked off.
In another instance, the so called “dead man's pedal” fails to operate and the train's main brakes can not be automatically applied. Such an incident occurred on May 16, 2001, when a train with 47 cars, some containing hazardous materials, traveled 66 miles unmanned through the state of Ohio.
Conventional rail skates are cast metal alloys that are designed to lift and carry the car wheels. If a railcar is moving at slow speeds and the rail skate is thrown under the wheel, or if the railcar is stationary but acted upon by an external force, the rail skate may slide along the rail, metal to metal, that may cause sparks and a potential fire. This is a potentially dangerous situation when tankers carrying petroleum or chemical agents are involved. Also, when the railcar is moving at slow speeds and the rail skate is thrown under the wheel, the rail skate jumps around violently has the potential to fall off the rail and provides no braking or “chocking” effect at all, putting the operator in a dangerous situation of trying to position another rail skate.
The servicing or the testing of the main air brakes can be more challenging when the railcar(s) have been disconnected from a source of compressed air for a period of time exceeding the so-called “hour rule” as stipulated in the Federal Railway Association (FRA) Regulations. When the railcar is already at rest, by design, the traditional rail skate does not prevent the railcar from potentially moving in small-unintended movements, for example when the handbrake is released by an inspector to inspect the brake components or functionality, especially if there is a small grade that has gone undetected by the inspector.
In some cases, the rail yard area or other areas where cars are located may be subject to vandalism where the brake system, either the air or the handbrake, may be compromised. The use of the traditional rail skate would be ineffective in such cases because it can be removed with relative ease.
French Patent No. 1,087,996 issued Sept. 17, 1953, to Dorrschuck, discloses a chock with torque arm component formed by two articulated arms (15,16) and a torque arm assembly (18,19). Because arms 15,16, are rotatably coupled this breaking system provides less rigidity and thus a less efficient breaking effect. In addition, because the torque arm (18,19) is rigidly attached to shoe (17) the torque arm is not capable to position the shoe (17) for simultaneous engagement of the wheel and of the travelling surface. In fact due to such lack of synchronism, shoe (17) needs rollers on the underside face to avoid “digging” and overrunning.
Accordingly, there is a need for an independent and fully automated chocking device which is physically attached to the vehicle while remotely actuated to provide constant braking effect for large wheeled vehicles.